MOSFET as a switch on GND pour PCB

Using Arduino General Electronics
1

hi all,

So i have a project that i would like to put on a PCB but there is a problem. I am using a MOSFET as a switch for cca 10 LEDs coming from 2 dev boards, breadboard prototype was all good as i could simply connect common GND of all LEDs to a MOSFFET and then use the control pin on one of the dev boards to control all LEDs (ON/OFF)

Now, with SMD PCB and GND pour on top layer, i've realized that this is not going to be the solution anymore...

I CAN NOT control LEDs from both dev boards, it has to be from only one, thus my original solution was to physically cut the GND to turn them ON or OFF, seemed like the simplest solution.

I am using EAGLE.

Any tips would be highly appreciated.

Many thanks,
Alek

2

Your description is a bit confusing, please post a tentative schematic, not a frizzy drawing. You can use P-Channel FETs for switching Positive and N-Channel FETs for switching negative (probably ground). What are cca 10 LEDs, can you supply a link?

3

Thanks gilshultz!

Yes, i am using N channel and as said, on breadboard everything works great.
"cca 10 LEDs" is 10 LED diodes, 5mm.
Now, i connect all negative leads of all LEDs together and then use N MOSFET to cut/connect LED ground to common ground, thus turning the LEDs ON or OFF. This is all great but now i want to move my design to PCB and i see a problem here as i have two planes poured on PCB, top "GND" and bottom "+5V".

Since my top plane is GND, how can i separate GND leads to LEDs so i can control them with MOSFET.
I was thinking to perhaps move GND signal through to the bottom power plane to connect to all LEDs...
OR, to somehow separate LED-MOSFET GND from main GND on top plane...

Many thanks,
Alek

4

Post your board (the eagle .sch and .brd files), lets see what you have.
The common anode will go to a power trace, the cathodes will connect in parallel to a the MOSFET which then connects to Gnd, yes? Eagle will separate those signals from the plane they are on.
If you use Edit:Net Classes, you can set the trace widths and clearance between traces and the planes.

5

CrossRoads:
The common anode will go to a power trace, the cathodes will connect in parallel to a the MOSFET which then connects to Gnd, yes? Eagle will separate those signals from the plane they are on.

Of course!!! Signal from MOSFET to cathodes will not be named GND and thus, will be separated from GND pour!
I wish this crossed my mind sooner instead of asking stupid questions! Thank you!
Thanks guys!
Alek

6

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.